Variable inductance device



Aug. 30, 1949. c. F. P. ROSE 2,480,340

VARIABLE INDUGTANCE DEVICE Filed Jan. 7, 1947 2 Sheets-Sheet 1 INVEN TOR CF. F. ROSE qaeM d A 7' TORNEV Aug. 30, 1949. c. F. P. ROSE 2,480,340

VARIABLE INDUCTANCE DEVICE Filed Jan. 7, 1947 2 Sheets-Sheet 2 'INVENTOR CE P. ROSE- A T TOBNEV Patented Aug. 30, 1949 VARIABLE INDUCTANCE DEVICE Charles F. P. Rose, Asbury Park, N. J., assignor to Bell Telephone Laboratories incorporated, New York, .N. Y., a corporation of New York Application January 7, 1947, Serial No. 720,545 6 Claims. (01. 171-242) This invention relates to variable electrical control devices and more particularly to variable electrical control devices of the type in which a relatively movable electrical coil and contact are provided.

The invention is applicable to variable inductance and variable resistance devices suitable for use as electrical control means in an electrical system.

An object of the invention is to provide an improved electrical control device operable as a means for controlling electrical inductance in an electrical system.

A feature of the invention resides in an electrical coil of spiral form.

Another feature resides in a contact means to frictionally engage required portions of turns of the spiral coil.

Another feature resides in a secondary contact means to engage and short circuit certain portions of the coil.

In the drawings:

Fig. 1 is a side view, partly in section, of a variable electrical control device embodying the invention;

Fig. 2 is an enlarged plan view, partly in section, of arms and contacts shown in Fig. 1;

Fig. 3 is a side view, partly in section, of certain parts shown in Fig. 2;

Fig. 4 is a view, partly in section, of portions of the coil and its support and a stylus contact in engagement with turns of the coil;

Fig. 5 is a view, in section, of portions of the coil and its support and a secondary contact in engagement with turns of the coil;

Fig. 6 is a plan view of the coil and its support but shows a contact structure and arrangement somewhat different from those shown in the previous figures; and

Fig. 7 is a side view, partly in section, of the device shown in Fig. 6.

In electrical systems in which high frequency currents are employed variable inductance coils are often provided to function as tuning elements in the system. The coil comprises a predetermined length of wire or other conducting material wound in a plurality of turns and a contact member to selectively engage the turns, the coil and the contact being relatively movable as required to bring more or less of the turns of the conductor into the electrical system.

In the present invention, as shown in Fig. l a. turntable 8 of insulating material is rotatably supported on a bearing assembly 9 mounted on an apertured base ll] of insulating material secured to a support H, the turntable 8 being secured to a rotatable shaft l2 extending through the bearing assembly 9. The shaft l2 and the bearing assembly 9 may be made of conducting material and be in conductive connection with a terminal I3 held in place on the bearing assembly 8 and the base II) by means of a holding nut I4. The shaft I2 is mechanically connected to a flanged bushing l5 which is secured to the turntable 8.

Supported on the turntable 8 is a spiral coil ii of a type commonly known as a pancake type coil. The spiral coil It may be a suitable length of conducting wire coiled to the required form, or, as shown in Fig.6, may be a conductor l'l of-ribbonlike form as shown in Fig. 7 and coiled in the form of a spiral and so that the turns thereof are in spaced relation. The spiral coil l l is mounted on the upper face of the turntable 8 in a substantially flat condition, lower edges of the turns being secured to the upper surface of the turntable 8 to hold the turns of the coil in required spaced relation and sothat two adjacent turns of the coil will cooperatively form, in effect, a track for a'stylus-like contact l8 shown in Figs. 1 and 3. Various means may be employed to securely mount the spiral coil I! on the turntable 8. I have found, however, that a convenient manner of mounting the spiral coil H on the turntable 8 is to secure the lower edges of the turns of the coil-to the upper surface of the turntable 8 by means of a suitable adhesive such for instance as a thermosetting insulating material l9 as shown in Fig. 7.

An inner end 20 of the spiral coil I1 is extended through a slot in a tubular cap 2| and across an upper end of the shaft l2. The tubular cap 2| is secured to the shaft l2 by means of a set screw 22 which extends transversely through the tubular cap 2|, a portion of the shaft 12 and into engagement with the inner end 20 of the coil 11. Mounting screws 23 are provided to secure the turntable 8 to the flanged bushing IS. A snubber pin 24 is secured in the turntable 8 and extended into engagement with the inner end portion 28 of the spiral coil IT to prevent undue strain on the inner end portion of the coil I1.

The stylus contact I8 is constructed and arranged to ride on and frictionally engage the turns of the spiral coil H. The lower end 25 of the stylus contact I8 is cone shaped and the point of the stylus contact [8 is arranged to extend into the space between turns of the coil. The stylus contact I8 is supported on the free end 28 of a curved arm 21 supported at one end on a rotatable post 28, a reduced lower end portion 29 of whichextends longitudinally into a recess 30 formed in the upper end of a pillar 3| rising from and secured to the base I0. A lower portion 32 of the pillar 3I is of reduced diameter and extends through an aperture in the base III. A nut 33 and lockwasher 34 are provided on the pillar 3| to hold the pillar 3I against withdrawal from the base III. A terminal 35 is secured to the pillar 3,I and is in electrical connection therewith. The reduced lower end portion 23 of the. rotatable post 28 is trapped against upward longitudinal withdrawal from the pillar 3I by means of a pin 38 extended transversely in the pillar 3| and into an annular groove 31 formed in the reduced lower end portion 29 of the rotatable post 28. Extending in spaced relation over the curved arm 21 is a bar 38 having one end portion secured to the top of the rotatable post 28 by means of a screw 33. The unsecured end of the bar 38 extends in spaced relation over the free end of the curved arm 21 and a spring 48 is disposed between the free end of the curved arm 21 and the unsecured end portion of the bar 38, the spring 40 and the bar 38 serving in cooperation to press the free end of the curved arm 21 toward the spiral coil I1 to keep the stylus contact I8 in good frictional engagement with the spiral coil I1.

When the turntable 8 is rotated the stylus contact I8 will move over the upper surface of the spiral coil I1 in continuous engagement with the turns in the spiral coil I1, the movement of the stylus contact I8 being imparted by the thrust of the turns in the spiral coil I1 against the conical end portion 25 of the stylus contact I8. If the stylus contact I8 is at the outer end of the spiral coil I1 and in engagement with the outer turn and the next turn inward thereof and the turntable 8 is suitably rotated to a suflicient extent the stylus contact I8 will travel from the outer end of the spiral coil I1 to the inner end of the spiral coil and will traverse all turns of the spiral coil I1 in succession, the stylus contact I8 being in continuous engagement with the spiral coil I1. A suflicient reverse movement of the turntable 3 will drive the stylus contact I8 back to its starting position.

When the terminal I3 is connected to one portion of an electrical system and the terminal 35 is connected to another portion of the electrical system the portions of the spiral coil 11 directly in the circuit will comprise the turns lying between the center of the spiral coil I1 and the innermost point of the spiral coil in instant engagement with the stylus contact I8. To minislightly more than completely over two adjacent turns in the spiral coil I1. Assuming that the arm 21 has been swung to its fullest inward extent the short-circuiting contact 52 will be resting on the two outermost turns of the spiral coil I1, the short-circuiting contact 5| will be resting on the next two turns inward and each .short-circuiting contact of the remainder of the set 41 will likewise rest on succeeding pairs of turns, the short-circuiting contact 42 being in frictional engagement with the two turns of the spiral coil I1 immediately outside the twoturns engaged by the stylus contact I8. When the stylus contact I8 is moving inwardly toward the center of the spiral coil I1 the short-circuiting contacts in the set 4I follow to keep the unrequired portion of the spiral coil I1 short-circuited to the arm 21 and hence to the terminal 35 by way of rotatable post 28 and the pillar 3|. As the free end 26 of the arm 21 swings to carry the stylus contact I8 toward the outside of the spiral coil I1 the short-circuiting contacts precede the stylus contact I8. When mize parasitic resonances of other portions of the spiral coil I1 not directly in the circuit a set of contacts designated by the general number M is provided. The function of the set of contacts 4| is to short-circuit the turns of the spiral coil I1 not instantly required in the system. The set M of contacts will be hereinafter called a set of short-circuiting contacts. In the set 4! of short-circuiting contacts shown in Figs. 1, 2 and 3 there are short-circuiting contacts 42 to 52 inclusive. Each short-circuiting contact comprises a disc portion 53 on the lower end of a stem portion 54 dimensioned to extend into a recess '55 formed in the arm 21. A spring 56 set in each recess and engaging the upper surface of the disc portion 53 of a short-circuiting contact serves to press the disc portion 53 of the short-circuiting contact toward the spiral coll I1. The disc portion 53 of each short-circuiting contact is dimensioned to simultaneously engage and extend the stylus contact I8 has been.moved outward to engage the two outermost turns of the spiral coil 11 the short-circuiting contacts in the set M also bear on the two outermost turns of the spiral coil I1, this being due to the curved form of the arm 21 and the curved arrangement of.the short-circuiting contacts.

The upper edges of the turns of the spiral coil I1 may at some points extend upwardly to dilferent heights due to manufacturing diiferences or to slight inaccuracies in securing the turns of the coil to the upper surface of the turntable 8. As shown in Fig. 4 portions of two turns '51 and 58 of the spiral coil I1 extend to different heights from the turntable 8 but since the point of the stylus contact I8 extends into the space between the two turns and the stylus contact I8 is of conical shape the two turns 51 and 58 are both in frictional engagement with the stylus contact I8. In Fig. 5 portions of two turns 59 and of the spiral coil I1 extend to different heights from the turntable 8 but since the short-circulting contact 42 has free motion to tilt in the recess 55 the disc portion 53 of the short-circuiting contact 42 may take a required slanting position to keep in frictional engagement with the two difierent height turns of the spiral coil I1.

In Figs. 6 and 7 means somewhat difierent from the means shown in the other figures for shortcircuiting unrequired portions of the spiral coil I1 are shown. In the structures and arrangements shown in Figs. 6 and 7 the turntable 8, the spiral coil I1, the arm 21, rotatable post 28, pillar 3| and terminal 35 may be the same as shown in previous figures of the drawings. In Figs. 6 and 7, however, a helical spring BI is provided to short-circuit instant unrequired turns of the spiral coil I1. It is advantageous to use the helical spring 8| rather than separate contacts when the spiral coil I1 is made of relatively small gage material and the turns are rather closely spaced. The helical spring 6| will hereinafter be called a short-circuiting spring 6|.

The short-circuiting spring BI is electrically connected at one end to the rotatable post 28 through a bolt 62 which extends through the rotatable post 28 and into a nut 53 secured to one end of the short-circuiting spring M. The other end of the short-circuiting spring BI is electrically connected through a nut 54 secured to that end of the short-circuiting spring and a bolt 65 extending through the stylus contact 68 which except for the aperture provided therein to accom- 6! against the spiral coil l1 spring pressed plungers 61, 68, 69, Ill, II, 12, 13 and 14 are mounted in the arm 21. Spaced recesses T are formed in the under surface of the arm 21 to accommodate the spring pressed plungers 61 to 14 inclusive. Each spring pressed plunger 61 to 14 inclusive comprises a plunger member 16 and a spring 11, part of the plunger member 16 being disposed in a recess and against a spring 11 located between the base of the recess I5 and the plunger member 16. The spring pressed plungers 61 to 14 inclusive bear downwardly against the upper surface of the short-circuiting spring 6| at spaced points and the lower end of each plunger member I6 is diametrically grooved to accommodate the engaged portion of the short-circuiting spring 6 l, the lower ends of the spring-pressed plungers 61 to 14 inclusive resting like saddles on the shortcircuiting spring GI and holding the short-circuiting spring 6| in a curved form following the curved form of the arm 21.

A leaf type spring 18 secured at one end by means of a screw 19 to the upper end of the rotatable post 28 and extending like a cantilever and sloping downwardly to the free end of the arm 21 provides spring pressure on the free end of the arm 21 to press the stylus contact 65 into good contact with the spiral coil l1. circuiting spring Gl keeps in contact with the turns of the spiral coil I! not instantly required in the circuit and short-circuits the unrequired turns to the terminal 35. A flexible conductor 80 connected at one end to the leaf spring 18 and at the other end to the terminal provides a good conducting lead between the leaf spring 18 and the terminal 35. The short circuit from the unrequired turns of the spiral coil ll may, therefore, be by way of the short-circuiting spring 6|, nut 64, bolt 65, stylus contact 66, arm 21, leaf spring 18 and flexible conductor 80 to the terminal 35.

What is claimed is:

1. A variable electrical control device comprising a rotatable coil of spiral form, a movable contact' driven by means of said coil and operable to select turns of said coil and bring the selected turns into a circuit, a curved movable support for said movable contact and extending over said coil and secondary contact means arranged in curved form and carried by said movable support and into contact with turns of said coil not selected, said secondary contact means being operable to short-circuit the turns of said coil that are not required in the circuit.

2. A variable electrical control-device comprising a rotatable conducting coil of spiral form, a movable stylus contact engageable with turns of said conducting coil and movable by means of said coil, curved supporting means for said stylus contact and operable to move over said conducting coil, said stylus contact being operable to control the number of turns in said conducting coil to be instantly used in a circuit and spring pressed short-circuiting contact means arranged in curved form and carried by said curved supporting means and engaging instantly unrequired turns of said conducting coil to short-circuit the The short- 2 6 instantly unrequired turns of said conducting coil.

3. A variable electrical control device comprising a rotatable conducting coil of spiral form, a movable stylus contact operable to fit between and selectively engage two adjacent turns of said conducting coil, said stylus contact being movable by means of said conducting coil, a curved movable supporting arm for said stylus contact and operable to carry said stylus contact over said conducting coil, said stylus contact being operable to selectively bring required turns of said conducting coil into a circuit and spring pressed short-circuiting contact means arranged in curved form and carried by said movable supporting arm into engagement with instantly unrequired turns of said conducting coil to shortcircuit the instantly unrequired turns of said conducting coil.

4. A variable electrical control devic comprising a rotatable coil of spiral form, a movable contact engaging and driven by means of said coil and operable to select turns of said coil to bring the selected turns into a circuit, a movable support for said movable contact and operable to travel over said coil and a set of spring-pressed contact members carried by said movable support into contact with the turns of said coil not selected by said movable contact, said set of spring-pressed contacts being of suflicient width to make contact with at least two turns to shortcircuit the turns of said coil that are not selected by said movable contact.

5. A variable electrical control device comprising a rotatable coil of spiral form, a movable con tact engaging and driven by means of said coil and operable to select turns of said coil to bring the selected turns into a circuit, a curved movable support for said movable contact and operable to travel over said coil and a helical spring contact carried by said curved movable support into Number engagement with turns of said coil not selected by said movable contact, said helical spring contact extending into contact with and operating to short-circuit the turns of said coil that are not selectively brought into the circuit by said movable contact.

6. A variable electrical control device comprising a turntable, a rotatable coil of spiral form mounted on the turntable, a movable arm extending over said turntable and said coil, said movable arm being curved to follow the curvature of said turntable, a stylus contact supported on said arm and in contact with said coil, said stylus contact being drivable across said coil by means of said coil to selectively bring into a circuit a required number of turns of said coil and movably supported. short-circuiting contact means carried by said arm and arranged in curved form corresponding to the curvature of said arm and operable to engage turns of said coil not brought into the circuit by said stylus contact.

CHARLES F. P. ROSE.

REFERENCES CITED The following references are of record intho file of this patent:

UNITED STATES PATENTS Name Date 1,485,482 Lowenstein Mar. 4, 1924 1,668,414 Martin May 1, 1928 1,896,269 Willoughby Feb. 7, 1933 2,382,470 De Rosa Nov. 14, 1844 

